The instant invention relates to a device for measuring the thickness of fiber slivers on drawing frames having a high production output without sacrificing quality.
Autoleveller drawing frames where a fiber sliver is scanned mechanically in order to ascertain fiber sliver thickness, and where the values found are converted into electrical signals are known. Such scanning devices are located before the actual drawing frame. They are used to scan the thickness of the arriving fiber sliver. Scanning is effected by means of scanning rollers. One of the two rollers is movably mounted and is moved out to a greater or lesser degree by the thickness fluctuations of the slivers. The measured voltage is transmitted to an electronic memory. The latter ensures that the drawing changes occur precisely at the instant when the deviating sliver segment is in the main drawing field. The change in draft is effected through a change in the rotational speed of the rollers of the draw frame. Such a known device is described in German Patent Publication DE-OS 25 44 029.
In addition to the scanning of the fiber sliver to be drawn, a method is known by which the drawn fiber sliver is scanned once more for control purposes. This is done by means of a pair of output roller installed at the input of the draw frame, independently of the scanning rollers. The drawn fiber sliver is scanned again, mechanically and a comparison between the desired and the actual value is made electronically from this mechanical scan. If an adjustable limit deviation is exceeded, the entire machine is stopped. This additional control, which is absolutely independent of the actual regulating system, is known under the name "sliver monitor". The limit of tolerance at which the machine is stopped has, normally, a value between 1 and 5% deviation. One of the two output rollers is mounted so that it can be moved out and serves as a scanning roller. The distance between the two draw-off rollers changes as a function of the volume of the fiber sliver. This distance is converted into an electrical signal by means of a position sensor and is transmitted to the monitor in the form of a measured magnitude. The monitor compares the measured magnitude with the 0% value set at the beginning. The machine is stopped if a deviation appears that is greater than the set limit value and longer than for a given delay period.
The goal in developing new drawing frames is to increase the output speed considerably. In this endeavor it has been found that a wider tolerance range of the fiber slivers must often be set with high production frames than with slow drawing frames in order to prevent automatic shut-off of the machine. It was, therefore, necessary to accept losses in quality as a consequence of the high output speed because a wider tolerance range had to be selected.